1. Field of the Invention
The present invention relates to a drive device for a railway vehicle, on which an energy storage device is mounted. More particularly, the present invention relates to a drive device for a railway vehicle, which can realize a function (hereinafter referred to as a high-speed range electric brake function) of extending a speed range for operation of a regeneration brake.
2. Description of the Related Art
In the field of railway vehicles, there has been widely used regeneration brake control in which a main motor is operated as a generator at the time of braking so as to convert the kinetic energy of the vehicle into electrical energy and return the energy to the overhead line while obtaining a braking force. The electric power returned to the overhead line by the regeneration brake control can be used as electric power to power the other vehicle to run, and hence the power consumption can be reduced.
However, a problem with the regeneration brake control is that sufficient braking force is not obtained because the regeneration performance is limited by the performance of the main motor or an inverter device in the high-speed range (higher than the terminal velocity of constant torque region).
A technique to solve this problem is described, for example, in Japanese Patent Laid-Open Publication No. 2008-278615 (Patent Document 1). The drive device for a railway vehicle includes a motor, an inverter device for driving the motor, a chargeable and dischargeable energy storage device, and a voltage adjustment device that uses the energy storage device as a power source to adjust the output voltage thereof by a chopper constituted by a current control device. The drive device is configured such that the energy storage device is connected in series with the inverter device, and such that a voltage resulting from adding the voltage generated by the voltage adjusting device to a DC power source voltage (overhead line voltage) is applied to the inverter device. Thereby, the voltage applied to the motor is increased so as to increase the output power of the motor, and hence the regeneration braking force in the high speed range can be increased without increasing the current of the motor.
However, in the technique described in Patent Document 1, the start timing of the chopper is not considered, and hence the technique has a problem that, when the inverter device performs the regeneration operation in a state where the chopper is not operated, that is, in the state where the switching element (current control device) of the chopper is turned off, the regeneration current always flows through the energy storage device so as to cause the energy storage device to be overcharged.
At this time, the voltage of the DC portion of the inverter device has a value resulting from always adding the voltage between terminals of the energy storage device to the DC power source voltage (overhead line voltage). Therefore, when an energy storage device, in which the voltage between the terminals of the energy storage device is not less than a voltage resulting from subtracting the DC power source voltage (overhead line voltage) from the withstand voltage of the inverter device, is used, the voltage of the DC portion of the inverter device exceeds the withstand voltage of the inverter device. Therefore, there is a design limitation that it is necessary to use an energy storage device in which the voltage between the terminals of the energy storage device is not more than a voltage resulting from subtracting the DC power source voltage (overhead line voltage) from the withstand voltage of the inverter device.
Further, there is also a problem that, when the regeneration operation of the inverter device is started and stopped in the state where the switching element of the chopper is turned off, the voltage of the DC portion of the inverter device has a value resulting from instantaneously adding and subtracting the voltage between the terminals of the energy storage device, as it is, to and from the DC power source voltage (overhead line voltage), and hence an over voltage and over current is also applied to the inverter device.
Therefore, an object of the invention is to prevent the over-discharge and overcharge of the energy storage device and further application of an over voltage and over current to the inverter device by adjusting the output voltage of the voltage adjustment device (current flowing through the energy storage device) by using the chopper which is surely operated at least during the operation period of the inverter device in such a manner that, when the power running operation or the regeneration operation of the inverter device is started, the operation of the chopper is started prior to the start of the power running operation or the regeneration operation of the inverter device, and that, when the power running operation or the regeneration operation of the inverter device is stopped, the operation of the chopper is stopped later than the stopping of the power running operation or the regeneration operation of the inverter device.